Inductive coupling

ABSTRACT

An inductive coupler includes a first transceiver electrically coupled to a first coil through a first tuning circuit. The inductive coupler may also include a second transceiver electrically coupled to a second coil through a second tuning circuit, where the second coil is positioned substantially concentric with the first coil.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application which claims priority fromU.S. utility application Ser. No. 15/174,813, filed Jun. 6, 2016, whichis hereby incorporated by reference in its entirety.

TECHNICAL FIELD/FIELD OF THE DISCLOSURE

The present disclosure relates to data and/or electrical powertransmission in a downhole tool.

BACKGROUND OF THE DISCLOSURE

When drilling a wellbore, data may be communicated between subcomponentsof a downhole tool. Because subcomponents may be located in differentstructures of the downhole tool, direct data connections may bedifficult to configure. Additionally, the downhole environment may causewear or damage to mechanical electrical connections. Mechanicalconnections such as rotary connectors may be expensive and may fail inthe downhole environment. Mechanical connections may also wear overtime, requiring maintenance operations to be performed. Mechanicalconnections may also be susceptible to fluid contamination.

For example, in a rotary steerable system (RSS), data may becommunicated between subcomponents of the RSS located in rotatingcomponents of the bottomhole assembly and subcomponents of the RSSlocated in nonrotating components of the bottomhole assembly.

SUMMARY

The disclosure provides for an inductive coupler. The inductive couplerincludes a first transceiver electrically coupled to a first coilthrough a first tuning circuit. The inductive coupler also includes asecond transceiver electrically coupled to a second coil through asecond tuning circuit, where the second coil is positioned substantiallyconcentric with the first coil.

The disclosure also provides for a downhole tool. The downhole toolincludes a collar with a primary collar and an intermediate collar and aprobe positioned within the collar. The downhole tool also includes acollar transceiver positioned within the primary collar, the collartransceiver electrically coupled to a male coil through a collar tuningcircuit. In addition, the downhole tool includes a probe transceiverpositioned within the probe, the probe transceiver electrically coupledto a probe coil through a probe tuning circuit. The downhole toolincludes a female coil positioned within the intermediate collar and acollar coil positioned within the intermediate collar. The collar coilis electrically coupled to the female coil through an intermediatetuning circuit.

The disclosure provides for a centralizer for supporting a probe withina collar of a downhole tool. The centralizer includes a centralizer bodyand an outer coil, the outer coil positioned at an outer surface of thecentralizer body. The centralizer also includes an inner coil, the innercoil positioned at an inner surface of the centralizer body, and theinner coil electrically coupled to the outer coil through a centralizertuning circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale. In fact, the dimensions of the variousfeatures may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 depicts an overview of a downhole tool in a wellbore.

FIG. 2 depicts a cross section view of an inductive coupler consistentwith at least one embodiment of the present disclosure.

FIG. 3 depicts a schematic view of the inductive coupler of FIG. 2.

FIG. 4 depicts a cross section view of an inductive coupler consistentwith at least one embodiment of the present disclosure.

FIG. 4A depicts a partial cross section perspective view of theinductive coupler of FIG. 4.

FIG. 5 depicts a schematic of a circuit including a tuning circuit of aninductive coupler consistent with at least one embodiment of the presentdisclosure.

FIG. 6 depicts a schematic view of a coil centralizer consistent with atleast one embodiment of the present disclosure.

FIGS. 7, 8, 9 depict perspective views of coil centralizers consistentwith at least one embodiment of the present disclosure.

DETAILED DESCRIPTION

It is to be understood that the following disclosure provides manydifferent embodiments, or examples, for implementing different featuresof various embodiments. Specific examples of components and arrangementsare described below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

FIG. 1 depicts an overview of a wellbore consistent with at least oneembodiment of the present disclosure. Wellbore 10 may be formed by drillstring 15. Drill string 15 may include drill bit 20 for forming wellbore10. In some embodiments, bottomhole assembly 100 may be positioned atthe end of drill string 15 within wellbore 10. In some embodiments,bottomhole assembly 100 may include one or more downhole tools 101.Although discussed with respect to drill string 15, one having ordinaryskill in the art with the benefit of this disclosure will understandthat the present disclosure may be utilized with any downhole tool 101without deviating from the scope of this disclosure and need not becoupled to a drill string. For example and without limitation, in someembodiments, downhole tool 101 may be positioned within wellbore 10 by adrill string, casing string, wireline, coiled tubing, or any othersuitable delivery mechanism.

In some embodiments, as depicted in FIG. 2, inductive coupler 103 may beutilized to transmit data between different subcomponents of downholetool 101 or between different downhole tools 101. Subcomponent, as usedherein, means any portion or subdivision of a tool. For example andwithout limitation, in some embodiments, inductive coupler 103 may beused to transmit information from collar 105 to probe 107. In someembodiments, collar 105 and probe 107 may be mechanically coupled suchthat they are rotatable relative to each other. In some embodiments,collar 105 and probe 107 may be mechanically coupled such that they arenot rotatable relative to each other. Although described as transmittingbetween collar 105 and probe 107, one having ordinary skill in the artwith the benefit of this disclosure will understand that inductivecoupler 103 may be used to transmit data between any two subcomponentsof downhole tool 101 or between different downhole tools 101.

With further attention to FIG. 2, in some embodiments, collar 105 mayinclude collar coil 109. Collar coil 109 may be electrically coupled tocollar transceiver 111 located in collar 105. In some embodiments, probe107 may include probe coil 113. Probe coil 113 may be coupled to probetransceiver 115. Transceivers 111 and 115 may be utilized to transmitand receive data transmitted inductively between collar coil 109 andprobe coil 113. In some embodiments, collar coil 109 and probe coil 113may be used for bilateral communication between collar 105 and probe107. In some embodiments, although described as transceivers 111 and115, one having ordinary skill in the art with the benefit of thisdisclosure will understand that one or both of transceivers 111 and 115may instead be solely a transmitter or receiver which utilizes collarcoil 109 and probe coil 113 for unilateral communication between collar105 and probe 107. In some embodiments, transceivers 111 and 115 mayhave separate transmitters or receivers.

In some embodiments, collar coil 109 and probe coil 113 may be alignedlongitudinally along downhole tool 101. In some embodiments, probe coil113 may be positioned at least partially radially within collar coil109. In some embodiments, collar coil 109 and probe coil 113 may begenerally coaxial. In some embodiments, collar coil 109 and probe coil113 may be formed from windings of wire such that when electric currentis passed therethrough, a magnetic or electromagnetic field is induced.Likewise, when a magnetic or electromagnetic field is passed throughcollar coil 109 and probe coil 113, an electric current is generated inthe coil. In some embodiments, transceivers 111 and 115 may beelectrically coupled to coils 109 and 113 respectively to generateelectric current in or receive electric current from coils 109 and 113to transmit data between collar 105 and probe 107.

In some embodiments, collar coil 109 and probe coil 113 may bepositioned away from magnetic or conductive materials. In someembodiments, without being bound to theory, eddy currents induced withinmagnetic materials may, for example and without limitation, reduce lossin the transmitted electric current. In some embodiments, void spacesbetween collar coil 109 and components of collar 105 and between probecoil 113 and components of probe 107 may be filled with a materialhaving high magnetic permeability and low electrical conductivity. Forexample and without limitation, in some embodiments, ferrites may beutilized. Ferrites, as understood in the art, may be ceramic compoundsof transition metals with oxygen, which are ferromagnetic butnonconductive. In some embodiments, high-magnetic permeability, lowconductivity steel may be used in the void spaces.

In some embodiments, collar transceiver 111 may be electrically coupledto collar coil 109 through collar tuning circuit 117. In someembodiments, probe transceiver 115 may be electrically coupled to probecoil 113 through probe tuning circuit 119. In some embodiments, byincluding tuning circuits 117 and 119 on both collar 105 and probe 107,inductive coupler 103 may be referred to as “double tuned”. In someembodiments, one or more tank circuits or resonant tank circuits may beutilized as tuning circuits 117 and 119. For example, one or more ofparallel tank circuits and series tank circuits may be utilized. Incertain embodiments, at least one parallel tank circuit and at least oneseries tank circuit may be used. As depicted in FIG. 3, in someembodiments, tuning circuits 117 and 119 may include one or morecomponents such as capacitors 120 a and 120 b. In some embodiments,capacitor 120 a and collar coil 109 may form a parallel resonant tankcircuit. In some embodiments, capacitor 120 b and probe coil 113 mayform a parallel resonant tank circuit. As depicted in FIG. 3, Rs and Rrrepresent the resistance of capacitors 120 a and 120 b and collar coil109 and probe coil 113 respectively. The resonant frequency of eachtuning circuit 117 and 119 may be given by:

$\omega = {\frac{1}{\sqrt{L_{1}C_{1}}} = \frac{1}{\sqrt{L_{2}C_{2}}}}$

where L1 is the inductance of collar coil 109, L2 is the inductance ofprobe coil 113, C1 is the capacitance of capacitor 120 a of collartuning circuit 117 and C2 is the capacitance of capacitor 120 b of probetuning circuit 119. By selecting capacitors 120 a and 120 b havingcapacitance based on the inductance values L1 and L2 of coils 109 and113 respectively, the resonant frequencies of tuning circuits 117 and119 may be equal or substantially equal, referred to herein as tuning orbeing tuned. In some embodiments, the resonant frequency of tuningcircuits 117 and 119 may be selected such that it correspondssubstantially with the expected transmission frequency for data betweencollar 105 and probe 107. In some embodiments, substantially equal asused herein may mean wherein the resonant frequencies of collar tuningcircuit 117 and probe tuning circuit 119 are within 5%, 1%, or 0.1% ofeach other. In some such embodiments, collar tuning circuit 117 andprobe tuning circuit 119 may be tuned at substantially one resonantfrequency or one resonant frequency band. In some embodiments, this maybe referred to as “single-tuned” circuits. In some embodiments, thetuned frequency may not be limited to one. In some embodiments, collartuning circuit 117 and probe tuning circuit 119 may be referred to as“dual-tuned”, and may, for example and without limitation, include oneor more secondary inductors and capacitors, which may allow collartuning circuit 117 and probe tuning circuit 119 to be tuned at tworesonant frequencies (e.g. a lower resonant frequency and higherresonant frequency). In some embodiments, the secondary inductor andcapacitor may form, for example and without limitation, a parallel LCtrap. In some embodiments, one of the resonant frequencies, for examplethe lower resonant frequency, may be used to transfer electrical powerthrough inductive coupler 103, while the higher resonant frequency maybe used to transfer electrical signals or data. In some embodiments,such a dual-tuned tank circuit may be a combination of parallel andseries resonant tanks. In some embodiments, the lower frequency may be,for example and without limitation, 20 Hz, 50 Hz, 60 Hz or 100 Hz. Insome embodiments, the higher frequency may be, for example and withoutlimitation, 500 Hz, 1 MHz, or 2 MHz.

In some embodiments, the mutual inductance M between coils 109 and 113may be given by:

M=k√{square root over (L ₁ L ₂)}

where k is the coupling coefficient between coils 109 and 113. In someembodiments, by increasing the mutual inductance M, the bandwidthavailable for data transmission about the resonant frequency of tuningcircuits 117 and 119 may be proportional to the mutual inductance M. Thecoupling coefficient k may be expressed as:

$k = \frac{M}{\sqrt{L_{1}L_{2}}}$

In some embodiments, such as for power transfer across inductive coupler103, the coupling coefficient k may be, for example and withoutlimitation, between 1.0 and 0.7. In some embodiments, such as for signalor data transfer, the coupling coefficient k may be, for example andwithout limitation, between 0.5 and 0.1. One having ordinary skill inthe art with the benefit of this disclosure will understand that thecoupling coefficients described herein are not intended to limit thescope of this disclosure. In some embodiments, such as for simultaneouspower and signal transfer, additional low-pass filters, high-passfilters, band-pass filters, and/or band-rejection filters may beincluded. In some embodiments, impedance-matching circuits such as, forexample and without limitation, additional transformers, may be usedwith the dual-tuned circuits.

In some embodiments, the mutual inductance M between two coils may begiven by:

$M = {\frac{N_{2}\Phi_{21}}{I_{1}} = {\frac{( {\mu_{0}\pi \; R_{2}^{2}} )}{2R_{1}}N_{2}}}$

where μ₀ is the magnetic constant, N₂ is the number of turns in thesecond coil, I₁ is the current in the first coil, R₁ is the radius ofthe first coil, and R₂ is the radius of the second coil where the secondcoil is larger than the first coil. Based on these equations, withoutbeing bound to theory, reducing the distance between the first andsecond coil may, for example and without limitation, increase mutualinductance M and may improve the coupling coefficient.

In some embodiments, data may be transmitted across a threadedconnection between subcomponents of downhole tool 101 or differentdownhole tools 101. For example, in some embodiments, as depicted inFIG. 4, downhole tool 101 may include primary collar 121 as a firstsubcomponent and intermediate collar 123 as a second subcomponent. Insome embodiments, primary collar 121 and intermediate collar 123 may be,for example and without limitation, parts of a motor, turbine, rotarysteerable system, MWD, LWD, or drill bit where probe 107 is a mandrel.Primary collar 121 may be coupled to intermediate collar 123 by threadedcoupling 125 having inductive coupler 127. Although depicted as part ofcollar 105, one having ordinary skill in the art with the benefit ofthis disclosure will understand that primary collar 121 and intermediatecollar 123 may be part of any component of downhole tool 101. Threadedcoupling 125 may, in some embodiments, include male coupler 129 andfemale coupler 131 formed on primary collar 121 and intermediate collar123 respectively.

As depicted in FIG. 4A, inductive coupler 127 may include male coil 133positioned on male coupler 129 and female coil 135 positioned on femalecoupler 131. In some such embodiments, when male coupler 129 is engagedwith female coupler 131, male coil 133 may be at least partially withinfemale coil 135. In some embodiments, male coupler 129 and female coil135 may operate as described herein above with respect to collar coil109 and probe coupler 113.

In some embodiments, collar transceiver 111 may be positioned in primarycollar 121 and collar coil 109 may be positioned in intermediate collar123. In some embodiments, inductive coupler 127 may transmit signalsgenerated by collar transceiver 111 or probe transceiver 115 acrossthreaded coupling 125. Although described with respect to a collar, onehaving ordinary skill in the art with the benefit of this disclosurewill understand that inductive coupler 127 may be utilized to transmitdata across any threaded connection without deviating from the scope ofthis disclosure.

In some embodiments, intermediate collar 123 may include intermediatetuning circuit 137. Intermediate tuning circuit 137, as depicted in FIG.5, may operate as described herein above with respect to tuning circuits117 and 119. In some embodiments, intermediate tuning circuit 137 mayinclude primary tuning circuit 139 a which may include one or morecomponents including, for example and without limitation, capacitor 141a and resistor 143 a. Primary tuning circuit 139 a may be used to tunefemale coil 135 to male coil 133 as previously described. In someembodiments, intermediate tuning circuit 137 may include secondarytuning circuit 139 b, which may be used to tune collar coil 109 to probecoil 113 as previously described. In some embodiments, intermediatetuning circuit 137 of intermediate collar 123 may operate passively, inthat intermediate tuning circuit 137 may include no power supply such asa battery within centralizer 145 (described hereinbelow). In someembodiments, intermediate tuning circuit 137 of intermediate collar 123may include a battery operated repeater. In some embodiments, asdiscussed herein above, intermediate tuning circuit 137 may include oneor more series tank circuits or parallel tank circuits. In someembodiments, as discussed herein above, intermediate tuning circuit 137may include one or more single-tuned tank circuits or dual-tunedcircuits.

In some embodiments, as depicted in FIG. 6, centralizer 145 may bepositioned between collar 105 and probe 107. Centralizer 145 may, forexample and without limitation, support probe 107 within collar 105.Centralizer 145 may include centralizer body 146. In some embodiments,centralizer body 146 may be formed from a nonmagnetic material such asrubber.

In some embodiments, centralizer 145 may be positioned such that it isat least partially within collar coil 109 and probe coil 113 is at leastpartially within centralizer 145. In some embodiments, centralizer 145may include outer coil 147 and inner coil 149. Outer coil 147 may bepositioned on or near outer surface 151 of centralizer body 146 andinner coil 149 may be positioned on or near inner surface 153 ofcentralizer body 146. In some embodiments, outer coil 147 and inner coil149 may be electrically coupled. In some embodiments, centralizer 145may allow signals and/or low-frequency power generated by collartransceiver 111 or probe transceiver 115 to be transmitted therethrough.

In some embodiments, centralizer 145 may include centralizer tuningcircuit 155. Centralizer tuning circuit 155, as depicted in FIG. 7, mayoperate as described herein above with respect to intermediate tuningcircuit 137 and may include one or more parallel resonant tanks. In someembodiments, centralizer tuning circuit 155 may include primary tuningcircuit 139 a which may include one or more components including, forexample and without limitation, capacitor 141 a and resistor 143 a.Primary tuning circuit 139 a may be used to tune outer coil 147 tocollar coil 109. In some embodiments, centralizer tuning circuit 155 mayinclude secondary tuning circuit 139 b, which may be used to tune innercoil 149 to probe coil 113. In some embodiments, centralizer tuningcircuit 155 may operate passively, such that centralizer tuning circuit155 may include no power supply such as a battery. In some embodiments,centralizer tuning circuit 155 may include a battery-operated repeater.

In some embodiments, as depicted in FIGS. 8, 9, centralizer 145 may begenerally annular. Centralizer body 146 may, in some embodiments, beformed from inner annular segment 157 and outer annular segment 159.Inner annular segment 157 may be mechanically coupled to outer annularsegment 159 by one or more radial spokes 161. For example, in someembodiments, as depicted in FIG. 8, inner annular segment 157 may bemechanically coupled to outer annular segment 159 by two radial spokes161. In some embodiments, as depicted in FIG. 9, inner annular segment157 may be mechanically coupled to outer annular segment 159 by threeradial spokes 161. In some embodiments, outer coil 147 may be positionedwithin outer annular segment 159 and inner coil 149 may be positionedwithin inner annular segment 157. In some embodiments, centralizertuning circuit 155 may be positioned within inner annular segment 157,outer annular segment 159, radial spokes 161, or a combination thereof.In some embodiments, radial spokes 161 may define flow paths (not shown)through which fluid may pass between probe 107 and collar 105 throughcentralizer 145.

In at least one embodiment of the present disclosure, an inductivecoupler for a downhole tool may include a first transceiver electricallycoupled to a first coil through a first tuning circuit and a secondtransceiver electrically coupled to a second coil through a secondtuning circuit, the second coil positioned substantially concentric withthe first coil. The first transceiver may be collar transceiver 111 orprobe transceiver 115. The first coil may be collar coil 109, probe coil113, male coil 133, female coil 135, outer coil 147, or inner coil 149.The first tuning circuit may be collar tuning circuit 117, probe tuningcircuit 119, intermediate tuning circuit 137, primary tuning circuit 139a, secondary tuning circuit 139 b, or centralizer tuning circuit 155.The second transceiver may be collar transceiver 111 or probetransceiver 115. The second coil may be collar coil 109, probe coil 113,male coil 133, female coil 135, outer coil 147, or inner coil 149. Thesecond tuning circuit may be collar tuning circuit 117, probe tuningcircuit 119, intermediate tuning circuit 137, primary tuning circuit 139a, secondary tuning circuit 139 b, or centralizer tuning circuit 155.

In some embodiments, the distance between adjacent coil pairs, such asbetween collar coil 109 and probe coil 113, mail coil 133 and femalecoil 135, outer coil 147 and collar coil 109, or inner coil 149 andprobe coil 113, may, for example and without limitation, be less than0.5″, less than 0.25″, or between 0.0625″ and 0.25″. In someembodiments, collar coil 109, probe coil 113, male coil 133, female coil135, outer coil 147, or inner coil 149 may be spaced between 0.125″ and0.5″ of the edge of the corresponding structure-collar 105, probe 107,male coupler 129, female coupler 131, outer surface 151, or innersurface 153 respectively.

The foregoing outlines features of several embodiments so that a personof ordinary skill in the art may better understand the aspects of thepresent disclosure. Such features may be replaced by any one of numerousequivalent alternatives, only some of which are disclosed herein. One ofordinary skill in the art should appreciate that they may readily usethe present disclosure as a basis for designing or modifying otherprocesses and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein. Oneof ordinary skill in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

1. A downhole communication system, comprising: a first transceiverelectrically coupled to a first coil through a first tuning circuit; asecond transceiver electrically coupled to a second coil through asecond tuning circuit; third and fourth coils, the third and fourthcoils being electrically coupled by an intermediate tuning circuit;wherein the third coil is inductively coupled to the first coil and thefourth coil is inductively coupled to the second coil.
 2. The downholecommunication system of claim 1 wherein the first transceiver ispositioned in an annular collar and the second transceiver is positionedin a probe and wherein the probe is positioned within the annularcollar.
 3. The downhole communication system of claim 2 wherein thecollar includes a primary collar and an intermediate collar, wherein thefirst transceiver is positioned within the primary collar, wherein thethird coil is a female coil positioned within the intermediate collar,and wherein the fourth coil is a male coil positioned within the primarycollar.
 4. The downhole communication system of claim 3 wherein theprimary collar is threadedly connected to the intermediate collar,wherein the threaded connection includes a male coupler and a femalecoupler, and wherein the male coil is positioned on the male coupler andthe female coil is positioned on the female coupler.
 5. The downholecommunication system of claim 2, further including a centralizer betweenthe collar and the probe, the centralizer having a centralizer body,wherein the third coil is a male coil, wherein the fourth coil is afemale coil, and wherein the third coil, fourth coil, and intermediatetuning circuit are all positioned within the centralizer body.
 6. Thedownhole communication system of claim 5 wherein the centralizer bodycomprises an inner annular segment and an outer annular segment and theinner and outer annular segments are mechanically coupled.
 7. Thedownhole communication system of claim 6 wherein the inner annularsegment and the outer annular segment define a fluid flow paththerebetween.
 8. The downhole communication system of claim 7 whereinthe fourth coil is positioned within the inner annular segment and thethird coil is positioned within the outer annular segment.
 9. Thedownhole communication system of claim 2 wherein the intermediate tuningcircuit comprises a primary tuning circuit and a secondary tuningcircuit and wherein the primary tuning circuit has a resonant frequencysubstantially equal to a resonant frequency of a tuning circuitpositioned in the annular collar, and the secondary tuning circuit has aresonant frequency substantially equal to a resonant frequency of atuning circuit in the probe.
 10. The downhole tool of claim 2 whereinthe first and second tuning circuits are dual-tuned, and signal andpower are transferred through the inductive couplings.
 11. The downholetool of claim 2 wherein the annular collar and probe are components of amotor, turbine, rotary steerable system, MWD, LWD, or drill bit and theprobe is a mandrel.
 12. A method for communicating in a downhole system,comprising: a) providing a collar that includes a first transceiverelectrically coupled to a first coil through a first tuning circuit; b)providing a probe that includes second transceiver electrically coupledto a second coil through a second tuning circuit; c) providing third andfourth coils, the third and fourth coils being electrically coupled byan intermediate tuning circuit; and d) inductively coupling the thirdcoil is to the first coil and inductively coupling the fourth coil tothe second coil.
 13. The method of claim 12, further includingpositioning the probe within the collar.
 14. The method of claim 12wherein the collar includes a primary collar and an intermediate collar,wherein the first transceiver is positioned within the primary collar,wherein the third coil is a female coil positioned within theintermediate collar, and wherein the fourth coil is a male coilpositioned within the primary collar.
 15. The method of claim 14 whereinthe primary collar is threadedly connected to the intermediate collar,wherein the threaded connection includes a male coupler and a femalecoupler, and wherein the male coil is positioned on the male coupler andthe female coil is positioned on the female coupler.
 16. The method ofclaim 12, further including providing a centralizer between the collarand the probe, the centralizer having a centralizer body, wherein thethird coil is a male coil, wherein the fourth coil is a female coil, andwherein the third coil, fourth coil, and intermediate tuning circuit areall positioned within the centralizer.
 17. The method of claim 16wherein the centralizer body comprises an inner annular segment and anouter annular segment and the inner and outer annular segments aremechanically coupled and define a fluid flow path therebetween.
 18. Themethod of claim 17 wherein the fourth coil is positioned within theinner annular segment and the third coil is positioned within the outerannular segment.
 19. The method of claim 12 wherein the intermediatetuning circuit comprises a primary tuning circuit and a secondary tuningcircuit and wherein the primary tuning circuit has a resonant frequencysubstantially equal to a resonant frequency of a tuning circuitpositioned in the collar, and the secondary tuning circuit has aresonant frequency substantially equal to a resonant frequency of atuning circuit in the probe.
 20. The downhole tool of claim 12 whereinthe first and second tuning circuits are dual-tuned, further includingthe step of transferring signal and power through the inductivecouplings.